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LingDy10 Feb 2012TUFS, Tokyo

David NathanEndangered Languages Archive

Hans Rausing Endangered Languages ProjectSOAS, University of London

Audio Theory and Practicefor Language Documentation

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Questions

have you recorded audio? have you published audio? what else have you done with your audio?

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Questions

you buy a recorder for $x. A matching microphone should cost:

(a) 3x (b) 0.8x(c) 0.3x (d) 0.1x (e) relative cost is irrelevant

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Question

Digitally recorded audio is better quality than analogue recorded audio because:

(a) digital microphones are more accurate (b) digital formats are more accurate (c) digital equipment is newer(d) digital formats capture more

information (e) no, digital audio is not better

than analogue audio

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Big questions

what are we actually recording? what/who is it for? what is the role of audio in language

documentation?

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Epistemology for audio in documentation

an audio recording is made in order to be experienced by a human listener

a recording conveys what a human listener would experience at a particular location in an event setting

documentation goals define recording methodology

a recording should capture spatial information metadata about the recording and the recording

setting are required for full interpretation ethical recording respects speakers and honours

their contribution through your effort and skill

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Evaluating recordings

accuracy: how well is the signal captured, as true to its sources and without distortion?

intelligibility/information accessibility: can the desired content be identified?

signal vs. noise: is the ratio acceptable? can the focal source be separated from all sources of noise?

listenability/comfort/aesthetics: is it easy on the ears? will it be debilitating to listen to for an extended time?

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Evaluating recordings

localisation of sources: is enough spatial information captured?

separation of noise: can all sources of noise be separated?

representation of environment: are the acoustic properties of the recording space appropriately represented?

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Evaluating recordings

content (identity, performance, uniqueness, coverage): were the right people recorded doing the right things?

editability/repurposeability: is the recording suitable for turning to relevant purposes?

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Recording audio

making it is both art and science a critical and ethical responsibility strongest relationship to communities it’s not necessary to record everything, but it

is necessary to record well

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SIGNAL & NOISE

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Evaluating recordings

signal noise signal to noise ratio listenability (eg comfort, consistency) fit for purpose

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Evaluating recordings

audio professionals use their human ears as evaluator of audio quality and value, while many linguists (mistakenly?) look to formats, spectrographs, wave-forms, analyses etc

44.1 KHz, 24 bit

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Signal - what you want

content contextual and spatial information fidelity comfortable to listen to

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Noise - what you don’t want

from environment: near: people, animals, activities far: traffic, generators, planes machines: refrigerators, fans, computers not hearable: mobile phones, electrical

interference acoustic: reflections/resonance

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Noise - what you don’t want

generated by (unwanted parts of) event shuffling papers, clothes table banging backchannel from interviewer equipment handling, especially

microphones and cables (and recorders with built-in mics)

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Avoiding handling noise

use stands and cradles etc

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Noise - what you don’t want

generated by equipment wrong input levels circuity noise (cheap or incompatible) compression loss or distortion ALC/AGC effects (pumping) video camera motors

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Evaluating environment/situation

external environment access electricity external noise sources

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External noise sources

example possibilities for dealing with it

traffic investigate, record in quiet time

face away

use damping materials

children get them involved

show something to satisfy curiosity

animals choose time of day

weather (wind, thunder, rain etc)

use dead cat; wait; reschedule

see also General principles

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Dead cat

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Close-up noise sources

machinesexample possibilities for dealing with it

refrigerator pre-survey what comes on intermittently

turn off

relocate

motors, switching monitor

fans monitor, dead cat (windshield)

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Dealing with noise sources

be prepared and aware seek collaboration monitor use or modify room acoustics

location direction surfaces reflection absorption isolation

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Utilising room acoustics

location away from doors, windows, traffic areas

direction face away from noise sources

reflection avoid parallel surfaces

surfaces avoid hard smooth surfaces choose or create soft or rough surfaces

isolation find an ‘’airtight’’ place

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When is a noise not a noise?

When it is part of the content, for some interpretation of the eventJohn Cage performance

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PERCEPTION & PSYCHOACOUSTICS

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Audio perception/psychoacoustics

a human listener has: location, orientation in a physical setting two ears - incredibly sensitive a brain/mind

the mind selects from various sources of sound and other sensory information, using long- and short-term memory

listening is actually a “hallucination”

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Psychoacoustics and recording

microphones don’t have a mind: they can't distinguish wanted from unwanted sound

microphones don’t have “edges” like camera lenses

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Psychoacoustics and recording

the recording process removes acoustic information

if you only care about transcription, then you are going to throw away over 99% of the acoustic information!

real worldrecord acoustic phenomenarepresent (some) linguistic componentsderive data

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Implications for recording

typical recording methods are unscientific! … so what should we do?

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Implications for recording

plan and manage recording goals equipment preparation environment and setup sources changes and actions settings

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Implications for recording

why is it important to record spatial information?

what other information (acoustic or non-acoustic) do we need?

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“Sound stage”

spatial information is an essential part of audio

we are amazingly attuned to it we should record in stereo

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“Sound stage”

... or in ORTF (binaural)

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MICROPHONES

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Microphones and audio quality

microphones are the greatest determinant of audio recording quality selection of appropriate microphone(s) for

the task placement and handling of the

microphone(s)

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Microphones in the digital era

microphones in the digital era recorder quality has increased but prices

decreased microphones have become comparatively

more expensive why? microphones are analogue devices!

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Microphone types

principle: dynamic vs condenser directionality: omni, cardoid, and shotgun spatiality: mono, stereo, binaural

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Microphone physical principles

dynamic generate signal from sound pressure more robust, less accurate used for musical and live performance

condenser more fragile, sensitive and accurate need power source - battery or phantom

power in general, use condenser microphones for

language documentation

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Omni

lavalier or tie-clip microphones are typically omni-directional

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Microphone directionality - omni

omni-directional

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Cardioid

many “standard” handheld microphones are cardioid units

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Microphone directionality - cardioid

cardioid

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Shotgun

shotguns are good for quiet sources, in some noisy environments, and for video work

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Microphone directionality - shotgun

shotgun/directional/hypercardioid

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Stereo microphones

spatial information is an essential part of audio

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Full “sound stage”: ORTF

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Simulating ORTF with 2 cardioids

17cm

110°

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Microphones - quality

generally, you get what you pay for each model has its own subjective colour decent microphones for language

documentation fieldwork cost from £120 to £300

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Reputable makers - include

AKG Audio Technica Beyerdynamic Røde Sennheiser Shure Sony

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Microphone placement

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Microphone usage principles

where should the microphone be? in general, about 20cm from the speaker’s

mouth

the inverse square law is your friend ...

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The inverse square law

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The inverse square law

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Using the inverse square law

if you have noise sources, maximise the signal to noise ratio by: placing the microphone as close as possible

to the signal source placing the microphone as far as possible

from the noise source

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AUDIO WORKFLOW

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Audio workflow

who/what/where /why/how do you want to record?

contact people

audio training

budget, research, and buy equipment

assemble, test, practise

Before you go

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Audio workflow

transport safely

check environment, situations, permissions

make test recordings

local training & collaboration

On site, before recording

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Audio workflow

record!

monitor!

collect metadata

(label) check quality

monitor

Sessions

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Audio workflow

(label) check quality

backup add information (metadata, metadocumentation, transcriptions, annotations, etc)

After sessions

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Audio workflow

… send samples to archive

add information (metadata, metadocumentation, transcriptions, annotations, etc)

... package and send to archive

Later

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CONNECTIONS

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Microphone connections

plugs cable types cables for stereo/mono, multiple wireless power sources for condenser microphones -

battery or phantom power

see http://www.hrelp.org/archive/advice/microphones.html

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Microphone connections

minijack/miniplug (fragile)

RCA/phono

1/4 inch (headphone)

XLR (Canon)

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XLR

professionals always use them electrical contact is independent of the

physical connection latching is independent of the electrical

contact

you can use XML-to-miniplug cables or converters for recorders with miniplug inputs

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IMPLICATIONS FOR VIDEO

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Implications for video

video captures spatial information – but so does audio

so these need to be co-ordinated match audio microphones and pattern to

video framing and events camera location is often not the correct

location for microphone get L & R channels correct!

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Implications for video

video formats for audio component may be compressed – how much does this matter?

don’t sacrifice audio quality for video should we record audio separately or not?

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IMPLICATIONS FOR METADATA

document the goals document the environment document the layout/setup

e.g. directional language use: diagrams, photos, oral and written

descriptions (e.g of relationships)

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End